The long-term goal of this research program is to validate in dogs a candidate vaccine against visceral leishmaniasis (VL) for evaluation in future clinical evaluations. We have recently described a powerful and reliable antigen discovery strategy to directly identify microbial vaccine candidate antigens in human bodily secretions. We combined RP-HPLC and mass spectrometry and categorized three distinct Leishmania infantum proteins presumably produced in parasite infected organs (liver/spleen/bone marrow) and excreted in the urine of patients with VL. The hypothesis underlying these studies was that microbial antigens found in vivo in the bodily fluids of the host are potentially effective vaccine candidate molecules because they represent microbial molecules abundantly produced in vivo that can be directly associated with the host defenses. The genes coding for these L. infantum proteins found in the patients' urine have been cloned, and the purified recombinant molecules have been obtained. Mice immunized with these proteins mixed with the adjuvant MPLA-SE developed robust Th1 response. Importantly one of these proteins induced strong protection in these animals after challenged with virulent L. infantum. The next and pragmatic challenge in the clinical translation of these findings is to expand these initial developmental studies and show that this novel molecule induces protective immunity in dogs, which are the ultimate animal model to test vaccine candidates for both human and canine VL.